=================================================================================
From:
http://blog.chinaunix.net/u/20754/showart_223337.html
---------------------------------------
#!/usr/bin/perl
#-----------------------------
#substr用来存取子串，可以修改子串，主要用法如下：
#$value = substr($string,$offset,$count);
#$value = substr($string,$offset);
#substr($string,$count) = $newstring;
#substr($string,$offset) = $newtail;
#-----------------------------
# 首先得到一个5个字符的字符串，然后跳过三个字符，分别得到2个8字符的字符串，最后剩下的给$trailing
#unpack/pack的用法以后会讲到，或者参见google 一下 ‘perl函数 unpack’
($leading,$s1,$s2,$trailing) =
??? unpack("A5 x3 A8 A8 A*",$data);
# 将字符串分成每5个字符一个串，存入数组@fives
@fivers = unpack("A5" x (length($string)/5),$string);
# 将字符串打散成单个字符，存入数组@chars
@chars = unpack("A1" x length($string),$string);
#-----------------------------
$string = "This is what you have";
# +012345678901234567890 Indexing forwards (left to right)
# 109876543210987654321- Indexing backwards (right to left)
# note that 0 means 10 or 20,etc. above
#下面是一些例子：
$first = substr($string,1); # "T"
$start = substr($string,5,2); # "is"
$rest = substr($string,13); # "you have"
$last = substr($string,-1); # "e"
$end = substr($string,-4); # "have"
$piece = substr($string,-8,3); # "you"
#-----------------------------
$string = "This is what you have";
print $string;
#This is what you have
substr($string,2) = "wasn't"; # 改变 "is" 为 "wasn't"
#This wasn't what you have
substr($string,-12) = "ondrous";# 替换最后12个字符
#This wasn't wondrous
substr($string,1) = ""; # 删除首字符
#his wasn't wondrous
substr($string,-10) = ""; # 删除最后10个字符
#his wasn'
#-----------------------------
# 你可以用 =~ 来测试子串，=~为正则表达式匹配运算符，后面会讲到，还可以google Perl 正则表达式
#主要是匹配则为True；否则为False。 pattern可以自己根据需要构造。
if (substr($string,-10) =~ /pattern/) {
??? print "Pattern matches in last 10 characters/n";
}
# 将 "is" 换为 "at",限制在最后五个字符；=~ s/// 为替换表达式。
substr($string,5) =~ s/is/at/g;
#-----------------------------
# 将字符串$a的第一个和最后一个字符交换
$a = "make a hat";
(substr($a,1),substr($a,-1)) = (substr($a,-1),1));
print $a;
# take a ham
#-----------------------------
# 抽取某些子串
$a = "To be or not to be";
$b = unpack("x6 A6",$a); # 跳过6个字符，抽取6个字符
print $b;
# or not
($b,$c) = unpack("x6 A2 X5 A2",$a); # 跳过6个字符,抽出2个字符的子串;后退5个字符,抽出2个字符的子串
print "$b/n$c/n";
# or
#
# be
#-----------------------------
#下面是一个综合的例子，主要是一个函数，实现了
#一种模板格式的输出。
sub cut2fmt {
??? my(@positions) = @_;
??? my $template = '';
??? my $lastpos = 1;
??? foreach $place (@positions) {
??????? $template .= "A" . ($place - $lastpos) . " ";
??????? $lastpos = $place;
??? }
??? $template .= "A*";
??? return $template;
}
$fmt = cut2fmt(8,14,20,26,30);
print "$fmt/n";
# A7 A6 A6 A6 A4 A*
#-----------------------------
=================================================================================
From:
http://blog.chinaunix.net/u/25264/showart.php?id=1412747
perl字符串处理函数
1，index
position = index (string,substring,position)
返回子串substring在字符串string中的位置，如果不存在则返回-1。参数position是可选项，表示匹配之前跳过的字符数，或者说从该位置开始匹配。
例子如下：
[root@localhost ~]# echo -n '/var/fap/test/123' | perl -ne '$rev=index($_,"a"); print $rev,"/n";'
2
[root@localhost ~]# echo -n '/var/fap/test/123' | perl -ne '$rev=index($_,"a",1); print $rev,3); print $rev,"/n";'
6
[root@localhost ~]# echo -n '/var/fap/test/123' | perl -ne '$rev=index($_,7); print $rev,"/n";'
-1
2，rindex
position = rindex (string,position)
与index类似，区别是从右端匹配。
例子如下：
[root@localhost ~]# echo -n '/var/ftp/tesa/123' | perl -ne '$rev=rindex($_,11); print $rev,"/n";'
2
[root@localhost ~]# echo -n '/var/ftp/tesa/123' | perl -ne '$rev=rindex($_,12); print $rev,"/n";'
12
[root@localhost ~]# echo -n '/var/ftp/tesa/123' | perl -ne '$rev=rindex($_,"/n";'
-1
[root@localhost ~]# echo -n '/var/ftp/tesa/123' | perl -ne '$rev=rindex($_,2); print $rev,"/n";'
2
3，length
num = length (string)
返回字符串长度，或者说含有字符的数目。
例子如下：
[root@localhost ~]# echo -n '/var/ftp/tesa/123' | perl -ne '$rev=length($_); print $rev,"/n";'
17
[root@localhost ~]# echo -n '/var/ftp/tesa/123 ' | perl -ne '$rev=length($_); print $rev,"/n";'
19
4，substr
substr (expr,skipchars,length)
抽取字符串（或表达式生成的字符串）expr中的子串，跳过skipchars个字符，或者说从位置skipchars开始抽取子串（第一个字符位置为0），子串长度为length，
此参数可忽略，意味着取剩下的全部字符。
当此函数出现在等式左边时，expr必须为变量或数组元素，此时其中部分子串被等式右边的值替换。
substr() 函数的作用有两个：替换一部分子串。 删除一部分子串。
例子如下：
[root@localhost ~]# echo -n '/var/ftp/test/123' | perl -ne '$rev=substr($_,9,);print $rev,"/n";'
test/123
[root@localhost ~]# echo -n '/var/ftp/test/123' | perl -ne '$rev=substr($_,4);print $rev,"/n";'
test
替换：
[root@localhost ~]# echo -n '/var/ftp/test/123' | perl -ne '$rev=substr($_,4)="hello"; print $rev,"/n";'
hello
删除：
[root@localhost ~]# echo -n '/var/ftp/test/123' | perl -ne '$rev=substr($_,4)=""; print $rev,"/n";'
5，lc，uc，lcfirst，ucfirst
lc，将字符串改为小写
uc，将字符串改为大写
lcfirst，改变字符串首字母小写
ucfirst，改变字符串首字母大写
例子如下：
[root@localhost ~]# echo -n 'hello,hanli' | perl -ne '$rev=uc($_); print $rev,"/n";'
HELLO,HANLI
[root@localhost ~]# echo -n 'HELLO,hanli' | perl -ne '$rev=lc($_); print $rev,"/n";'
hello,hanli
[root@localhost ~]# echo -n 'hello,Hanli' | perl -ne '$rev=ucfirst($_); print $rev,"/n";'
Hello,Hanli
[root@localhost ~]# echo -n 'hello,Hanli' | perl -ne '$rev=lcfirst($_); print $rev,Hanli
